1. Field of the Invention
The present invention relates to a manufacturing method of semiconductor devices and to a semiconductor device. In concrete, the present invention relates to a manufacturing method of bipolar transistor semiconductor devices that is formed on a semiconductor substrate on which an isolation structure is formed with insulating layer, and to a bipolar transistor semiconductor device.
2. Description of the Related Art
FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, FIG. 2E, FIG. 2F, FIG. 2G, and FIG. 2H are diagrams showing one example of a manufacturing method of a existing bipolar transistor. The existing bipolar transistor B can be manufactured as shown in FIG. 2A with a semiconductor substrate 51 in which an isolation structure is formed by a first insulating layer 53 consisting of silicon oxide.
That is, all over a surface of the semiconductor substrate 51, for instance, a substrate of a single crystal of p-type silicon, an impurity such as Sb or the like is implanted to form a collector electrode layer 52. Above a surface of a central area thereof, an active area 54 of which upper surface is exposed is disposed and this active area is doped by an impurity of low concentration to form a collector layer. The surroundings of the collector layer is insulated and isolated from the surrounding elements or the like, for instance surrounding active areas, by a first insulating layer 53 that is formed by the use of, for instance, LOCOS method or the like.
Upon manufacturing a bipolar transistor B, first, a silicon layer 55 is formed all over the surface of the semiconductor substrate 51 by non-selective epitaxial growth method. Thereby, as shown in FIG. 2B, on the first insulating layer 53 a first poly-silicon layer 57 is formed to be a part of a base electrode. Simultaneously therewith, on an upper surface of the active area 54 a first epitaxial layer 56 is formed to be a base layer.
Further, all over the surface of the semiconductor substrate 51 a silicon oxide layer is formed to be an insulating layer. As shown in FIG. 2C, this insulating layer is patterned to form a second insulating layer 58 to be a buffer layer over from an upper surface of the first epitaxial layer 56 to an upper surface of the first poly-silicon layer 57.
Next, as shown in FIG. 2D, all over the surface of the semiconductor substrate 51, a second poly-silicon layer 59 that contains an impurity such as B or the like in high concentration is formed to be a base electrode. Further, on the second poly-silicon layer 59 a third insulating layer 60 consisting of silicon oxide and a fourth insulating layer 61 consisting of silicon nitride are stacked to be an interlayer film.
Thereafter, as shown in FIG. 2E, an opening for pulling out an emitter layer 66 is opened, while positioning it at an approximate center of the second insulating layer 58, in the second poly-silicon layer 59 and the third and fourth insulating layers 60 and 61 by the use of anisotropic etching method. At this time, the opening 62 is opened to stop on the second insulating layer 58.
Thereafter, as shown in FIG. 2F, on an inner surface of the opening 62 a fifth insulating layer 63 is formed with silicon nitride. Then, another opening 64 is opened in the second insulating layer 58 by the use of anisotropic etching method to expose a first epitaxial layer 56.
Then, as shown in FIG. 2G, a third poly-silicon layer 65 that becomes an emitter electrode layer and contains an impurity such as Sb or the like in high concentration is formed inside the openings 62 and 64 so that a part thereof is positioned on an upper surface of the fourth insulating layer 61. Thereafter, thermal treatment is applied to form an emitter layer 66 inside the first epitaxial layer 56.
Finally, after a sixth insulating layer 67 consisting of silicon oxide is patterned all over the surface of the semiconductor substrate 51, a wiring 68 for pulling out an emitter electrode (the third poly-silicon layer 65) is formed. Thereby, a bipolar transistor B such as shown in FIG. 2H can be manufactured.
However, in a bipolar transistor B manufactured as described above, a base electrode layer is constituted of a first poly-silicon layer 57 that contains impurity of low concentration and a second poly-silicon layer 59 that contains impurity of high concentration. A base layer (the first epitaxial layer 56) has a structure to pull out through connection with the first poly-silicon layer 57 formed in the surroundings thereof.
The first poly-silicon layer 57 is, being formed on the first insulating film 53 by the use of non-selective epitaxial growth method, a polycrystalline layer. Moreover, since impurity concentration thereof can not be made high, a base resistance becomes substantially high. As a result of this, the transistor is retarded in operation of high speed and power consumption thereof increases.
Further, when an opening 62 is formed to pull out an emitter layer 66, if there occurs a discrepancy in alignment of a mask during photolithography, the opening 62 is formed at a position deviated from the center of the area of the second insulating layer 58. As a result of this, there is a concern that an emitter layer 66 that is formed later is liable to approach or connect electrically to the first poly-silicon layer 57 that is a base electrode layer. Accordingly, there is a problem that an withstand voltage deteriorates and leakage occurs between base-emitter.
In particular, since the opening 62 is preferable to be formed at an approximately identical area with an active area 54 and a base layer is formed only on an upper surface of the active area 54, a precise alignment of a mask is required. In addition, when a semiconductor device is made small, the active area is required to be small, and this is an increasingly important problem.
Further, FIG. 3A, FIG. 3B, FIG. 3C, FIG. 3D, FIG. 3E, FIG. 3F, and FIG. 3G are diagrams showing another existing manufacturing method of a bipolar transistor.
A base electrode layer of a bipolar transistor C manufactured according to the manufacturing method is, as shown in FIG. 3G, constituted so that it is pulled out from an upper surface of the base layer. The bipolar transistor C can be, as shown in FIG. 3A as identical as the aforementioned bipolar transistor B, manufactured with a semiconductor substrate 71 on which an isolation structure is formed with a first insulating layer 73 consisting of silicon oxide.
First, as shown in FIG. 3B, all over the semiconductor substrate 71 a second insulating layer 75 is formed to form a buffer layer. Then, on an upper surface of the second insulating layer 75 a first poly-silicon layer 76 that is a base electrode layer containing impurity in high concentration, a third insulating layer 77 that consists of silicon oxide and is an interlayer film, and a fourth insulating layer 78 consisting of silicon nitride are stacked.
Thereafter, as shown in FIG. 3C, an opening 79 for pulling out an emitter layer 83 is opened, while positioning on an approximate center of the active area 74, in the first poly-silicon layer 76, a third insulating layer 77, and a fourth insulating layer 78 by the use of anisotropic etching method. At this time, the opening 79 is stopped on the second insulating layer 75.
Then, as shown in FIG. 3D, on an inner surface of the opening 79 a fifth insulating layer 80 consisting of silicon nitride is formed. Thereafter, the second insulating layer 75 is etched to form a cavity 81 inside the second insulating layer 75 and expose the active area 74.
Thereafter, as shown in FIG. 3E, inside the cavity 81 an epitaxial growth layer 82 is formed by the use of epitaxial growth method to form a base layer.
Then, as shown in FIG. 3F, a second poly-silicon layer 84 containing impurity such as Sb or the like in high concentration is formed inside the opening 79 so that part thereof is located on an upper surface of the fourth insulating layer 78 to form an emitter layer. Thereafter, heat treatment is implemented to form an emitter layer 83 inside the epitaxial growth layer 82.
Finally, all over the surface of the semiconductor substrate 71 a fifth insulating layer 85 consisting of silicon oxide is patterned. After that, a wiring 86 for pulling out an emitter electrode layer outside is formed. Thereby, a bipolar transistor C such as shown in FIG. 3G can be manufactured.
According to this method, a base layer (epitaxial growth layer 82) is formed inside a cavity 81 opened in a second silicon oxide film. Accordingly, the base layer can be constituted of an epitaxial growth layer 82 containing impurity in high concentration. At this time, since the base electrode layer (the first poly-silicon layer 76) contains impurity of high concentration, resistance of the base layer can be substantially decreased.
In addition, a base layer, after the opening 79 is formed for the emitter electrode layer, is formed a cavity 81 in an area larger than the opening 79. Accordingly, even if there is a discrepancy in alignment of a mask during photolithography when the opening 79 is formed, between the side edge of the base layer and the emitter layer 83 a sufficient distance can be secured. Accordingly, sufficient withstand voltage can be secured between base-emitter.
However, according to this method, a cavity 81 that is used to form a base layer becomes, being formed by etching, an area larger than the opening 79 that pulls out the emitter layer 83. Accordingly, when the opening 79 is formed on the approximately same area as the active area 74, even the first insulating layer 73 is etched and removed. As a result of this, the junction area of base-collector becomes wide to increase a capacitance of base-collector. Therefore, there are problems that the fast response property of the transistor is deteriorated and power consumption is increased.
The present invention is carried out to solve such problems. An object of the present invention is to provide a manufacturing method of a bipolar transistor that can reduce deterioration of withstand voltage or leakage between base-emitter without increasing capacitance between the base-collector.